One of the authors told the BBC there was evidence of government involvement. Damascus has denied claims of abuse.
The investigators examined thousands of images of dead prisoners reportedly smuggled out of Syria by a defector.
The report comes a day before peace talks are due to begin in Switzerland.
The Guardian – which along with CNN first unveiled the report – says the latest claims of torture and executions appear to have been timed to coincide with the conference, in the resort town of Montreux.
The talks are being seen as the biggest diplomatic effort to end the three-year conflict.
More than 100,000 people have been killed and millions more displaced in the war.
The report was commissioned by Qatar, which supports Syrian rebels. It is based on the evidence of a military police photographer, referred to only as Caesar, who reportedly leaked about 55,000 digital images of 11,000 dead detainees after he defected.
He told investigators his job had been to take photographs of corpses, to allow a death certificate to be produced, but did not claim to have witnessed killings or torture himself.
“There could be as many as 50 bodies a day to photograph which require 15 to 30 minutes of work per corpse,” he is quoted as saying.
The photographs cover the period from the start of the uprising in 2011 until August last year.
Investigators say most of the bodies in the photos were emaciated; many had been beaten or strangled.
One of the authors of the report, Professor Sir Geoffrey Nice told the BBC’s Newsday programme that the scale and consistency of the killings provided strong evidence of government involvement that could support a criminal prosecution.
Forensic pathologist Stuart Hamilton also examined the evidence and told Newsday that in the images that he saw, a large number of detainees were showing “evidence of significant starvation”.
He said that many looked as if they had been bound or restrained.
“There were a large number who had been beaten. And there were a significant minority who had clearly been strangled,” he said.
The BBC’s Jim Muir in Beirut says if the account is to be believed, it shows a chilling systematic documentation of the bodies, each of which was given a number.
The Syrian government has not commented on the report, but has denied accusations of human rights abuses during the 34 months of the conflict.
The planned Montreux talks are back on the agenda after the UN Secretary-General withdrew an invitation to Iran to join the conference.
UN spokesman Martin Nesirky criticised Tehran for failing to support the plan to form a Syrian transitional government, which is the basis of the conference.
The invitation to Iran, a key ally of the Syrian regime, had angered the US and the Western-backed Syrian opposition.
The government and the main exiled opposition group, the National Coalition, are due to send delegates to the conference on Wednesday.
The National Coalition had threatened to pull out if the invitation to Iran was not rescinded, but they have since confirmed that they will now be attending.
Withdrawing the invitation was “the right thing to do”, Monzer Akbik, the National Coalition’s chief of staff, told the BBC.
It is unclear whether Iran will be able to join the talks two days later, when they move to Geneva.
US officials welcomed the withdrawal, saying they hoped the focus could return to the content of the talks.
The conference is the culmination of months of diplomacy. In May last year, Russian and the US agreed to try to bring both sides together.